Why Are My Dog’s Nipples Enlarged After Heat?

When you get yourself a dog, you’re entering new territory and there’s nothing more mystifying than your pet’s reproductive cycle and everything associated with it.

If your pet hasn’t been spayed yet, you’ve probably been told to expect her going into heat.

Some vets do recommend allowing a bitch to go through a first heat cycle before spaying.

According to your calculations she’s out of it now, and yet her nipples are still enlarged. Why is that? Is it dangerous? What can you do about it?

There’s nothing to worry about. It’s a perfectly natural thing and it will go away.

However, you’ll have to keep an eye on your dog just in case those enlarged nipples are a sign of a health issue.

So, let’s have a quick look at the main things you need to know about a dog’s heat cycle and what those enlarged nipples might mean.

What are the stages of a dog’s heat cycle?

OK, let’s start with the basics.

A female dog will experience her first heat cycle once she reaches puberty. This may vary depending on the dog’s breed.

While the average age a bitch goes into heat for the first time is six months, smaller breeds become sexually mature earlier than that.

On the other hand, a female of a large breed might not reach puberty until she is 18-24 months.

A dog’s heat cycle consists of four stages. For a pet owner, it’s the first two stages that are of interest, and they’re called proestrus and estrus.

Proestrus is the stage the dog’s body starts preparing for breeding and there are few signs to alert the owner of what’s going on.

It is at this time that estrogen levels rise, but the female is not yet interested in male dogs. This stage can last up to nine days and your pet might be a bit more agitated.

Estrus is the period during which a female dog is actively looking for male partners as she is becoming fertile.

Estrogen levels drop, but progesterone levels start to rise as the dog’s body is preparing for a potential pregnancy.

The first thing you might notice is the bloody discharge.

This can be very confusing if you compare this stage with human physiology. While women are not fertile during their period, things are completely different with dogs.

At first, the discharge will be bloody, but it becomes more watery over the next few days.

The eggs are released at this point and the dog is ready for breeding.

It is also at this time that you will notice a significant swelling of the vulva and the mammary glands, hence the enlarged nipples.

You’ll notice your dog pees more often and she’s marking the territory. Her urine is full of pheromones letting male dogs know she’s looking for a mate.

The estrus stage can last between 9 and 14 days.

Diestrus is the moment your dog goes out of heat.

The progesterone levels in her body are still high, but she’s no longer interested in mating and will no longer welcome male attention.

The dog’s vulva and nipples will still be enlarged as her body is still full of progesterone.

This stage can last up to two months so there’s no reason to worry about your dog’s enlarged nipples. The swelling will subside eventually.

Anestrus is basically the quiet period where hormone levels are back to normal and the female couldn’t care less about male dogs.

Her vulva and nipples will return to their original size more or less. According to experts, your dog’s nipples won’t return to being as small as they were before entering puberty.

Anestrus lasts for 2-3 months and then the female goes into heat again.

Large breeds only go into estrus once a year, but for small breeds it’s not uncommon to go through 2 or 3 heat cycles during a 12 months period.

What is a false pregnancy?

One of the main reasons your dog’s nipples might be seriously enlarged after heat is that she thinks she’s pregnant.

This is what doctors call false pregnancy and it can happen to any female, whether she has mated or not.

You might notice your dog is gaining weight and her nipples will be visibly swollen. She might even start producing milk, although that’s not always the case.

You’ll also notice a distinct nesting behavior, as the dog prepares to give birth to an imaginary litter.

In some cases, the female will go through a fake birth and you’ll see her straining to bring those non-existent puppies into this world. She might also display a protective behavior towards other puppies or even kittens.

Typically, a false pregnancy resolves itself after a few weeks and there’s very little you can do about it, except bear with her.

You should check out her nipples every now and then, especially if she starts producing milk.

The nipples and the underlying tissue may become quite inflamed and painful.

Accumulation of milk in the mammary glands is called galactostasis, and it’s a common condition associated with a false pregnancy or the weaning period of a bitch who has had puppies.

If you notice they’re causing her visible discomfort, speak to your vet.

Your dog might need medication to reduce inflammation and the vet might also teach you how to apply ice packs to help relieve the pain.

What if…?

Don’t assume your dog is going through a false pregnancy just because you don’t think she has mated.

Unless you’ve kept an eye on her during the whole estrus stage, you don’t know that.

She might have had some fun while you thought she was sleeping under her favorite tree in the backyard.

A male dog will do anything to get near a bitch in heat and that fence of yours might not be enough to stop him.

Just so you know, during a real pregnancy a dog’s nipples will become enlarged and darker in color.

Towards the end of the pregnancy, they will become discolored and there will be a milky discharge.

What is mastitis?

Mastitis is another common condition, usually associated with nursing dogs.

If the puppies bite or tear at their mother’s nipples this can trigger an infection. However, it’s not only nursing dogs that can develop mastitis.

It can also happen during a false pregnancy, and in some cases even male dogs can develop an infection of the mammary tissue.

If the nipples are very swollen and painful, you might also notice a reddish discharge.

Take your dog to the vet as she’ll need antibiotics to treat the infection before it spreads.

In extreme cases, one or more of the mammary glands may have to be surgically removed.

Why does my dog have lumps under her nipples?

Any pet owner can understand swollen nipples are a normal part of an intact dog’s female cycle.

However, the moment the owner feels there’s a lump under the dog’s nipples they instantly fly into a panic.

Everyone knows tumors are bad and your first thought will be cancer.

However, that is not always the case.

In fact, it is normal for certain lumps or masses to appear during your dog’s heat cycle.

They are caused by the high progesterone levels, but the good news is that they will disappear once the hormone levels revert back to normal.

Benign or malignant tumors

On the other hand, lumps are not something you want to ignore, as they can be malignant.

In most cases, these lumps which can reach 2 or 3cm in diameter affect the fourth and fifth nipples, those closer to the groin.

If the lumps do not disappear after the dog is no longer in heat, it is important that you take your pet to the vet.

The doctor will probably perform a Fine Needle Aspiration (FNA) or a biopsy, extracting cells from the lump to determine if it’s a benign tumor or a malignant one,

The problem is that a dog can very well have a benign and a malignant tumor at the same time.

Also, it is impossible to predict how a benign tumor will behave over time. Some tumors may remain unchanged for years, while others can become malignant over time.

If your dog has any type of mammary tumor, the vet will most likely want to have it removed just to be on the safe side.

Malignant tumors are rare in spayed dogs who do not experience changes in hormone levels.

Experts believe progesterone plays an important part in the abnormal proliferation of breast tissue.

If your dog is intact at the time a tumor, be it benign or malignant, is discovered, the vet will probably recommend spaying her at the same time as the abnormal growth is removed.

Closing Thoughts

It is quite normal for a female dog to have swollen nipples once she goes into season.

While a season only lasts for 21 days on average, her nipples may appear enlarged for several weeks more.

Once the progesterone levels in her body start dropping, her nipples should be back to normal, or almost normal, as they won’t return to the size they were before the first heat cycle.

If you notice any sign of inflammation or infection, take your pet to the vet as she may have developed mastitis.

If you discover a suspicious lump near your dog’s nipple, have it checked out as soon as possible.